I recently upgraded to 2 BTL 15s from a 2 Qs. In a nutshell im having the same problems that i was having with the Qs, Overexcursion. I am running a MTX TA81001 to each sub, only 1500 watts. The total volume of the box after displacements is 8.5 cubes, port is around 100sq inches and is tuned to 32hz. SSF is set at 30hz, HPF is set at 150hz, Bass boost is set at 0, and volt meter reads 38 volts which should make the amp put out 1500 watts. I went to my local shop (Pure Pressure Audio) where everyone who works there runs FI. They said i need 6 or more cubes for each speaker, and my box is causing them to move as much as they are. I built the box to FIs specs and it doesnt sound right. Can anyone help me.

High pass filter? You mean low pass filter, yes?

Does that shop have an oscilloscope?

High pass filter? You mean low pass filter, yes?

Does that shop have an oscilloscope?

Yes, low pass filter. No, they dont have a scope. none of the shops have a scope, they all told me to use a volt meter.

you're supposed to set your lpf 3-5hz lower than the tuning of the box!

Edited April 4, 200817 yr by nick_da_quick808

you're supposed to set your lpf 3-5hz lower than the tuning of the box!

You mean the subsonic filter

And if his SSF was set too high, that would actually help with the problem he's experiencing...

I have a feeling it's due to not knowing how much power is actually being sent to the driver...have you at least clamped it at a specific frequency?

Im not sure what clamped means. I played a 50hz test tone at 0dbs when i set it with a meter. I cut about 6 inches off the port to see what would happen and it only made the problem worse (higher excursion on a 30 hz tone). It seems like the lower the tuning the less it moves on lows. should i try tuning at 30hz.

The voltmeter is only telling you one component of the output power. If you put a true RMS clamp meter on one of the leads going to the sub, you'll have the other that you need...the actual current being sent to the driver at that specific frequency. And if that shop doesn't have one of those, it's time to find people that know what they're doing

It seems like the lower the tuning the less it moves on lows.

Cone movement is going to be at its minimum right around the tuning frequency. By cutting off port length, you increased the tuning frequency, so the driver has more of a chance to unload below tuning...

Thanks for all your help, ill keep playing with it untill i figure something out.

Can you post up you box and port dimensions. . .

I never had problems with my BTL's going over 2" peak to peak. . .

Brian

Im not sure what clamped means. I played a 50hz test tone at 0dbs when i set it with a meter. I cut about 6 inches off the port to see what would happen and it only made the problem worse (higher excursion on a 30 hz tone). It seems like the lower the tuning the less it moves on lows. should i try tuning at 30hz.

Because you did this, you probably have no idea what it's tuned to now.

The sub, as mentioned before, will not move as much right at tuning so don't be worried that you are not getting proper output...

Because you cut off part of the port, you've made it harder to fix the problem now.

The box is now tuned higher which means you will need to increase your SSF probably resulting in more low bass response being lost.

And you got your LPF set so high, i'm wondering if it's moving to much in the higher range.

Your sub, if it is ever gonna move too much, will happen more frequently right below tuning if SSf is set too low or if moving too much on higher notes, it needs less power going to it based on box design.

I know of no one who sets the LPF that high, that's crazy. Drop it down to 90 at least if not more.

I feel really stupid for posting this and im sorry for wasting everyones time. I went up to the shop and they told me there is no way btls could bottom out with that power. They said they are bottoming out because i am listening to them with the trunk open and there is no pressure coming from the trunk lid. This is the first system ive ever had in a car and i felt like an idiot when i realized how much sense it made. the inside of the car sounds rediculous and these are some of the best speakers ive ever heard. I appreciate everyones input.

ok, go to another shop, you're not an idiot, they just proved they were the idiots!

Playing your stereo with the trunk open causes subs to bottom out?

Wow, wonder why companies never put in their little warranty notice not to open your trunk while playing???? Maybe because that's Ghetto BS.

Stick with gettin your info from here if they got people that retarded where you are.

And give me a BTL, i bet i can get it to bottom out with that amp easy.

Build a 7cuft box tuned at 60hz with no SSF playing 10hz tones.... wonder what would happen... hmm.

ok, go to another shop, you're not an idiot, they just proved they were the idiots!

Playing your stereo with the trunk open causes subs to bottom out?

Wow, wonder why companies never put in their little warranty notice not to open your trunk while playing???? Maybe because that's Ghetto BS.

Stick with gettin your info from here if they got people that retarded where you are.

And give me a BTL, i bet i can get it to bottom out with that amp easy.

Build a 7cuft box tuned at 60hz with no SSF playing 10hz tones.... wonder what would happen... hmm.

But this was a 4cuft box tuned to 32hz on half the power that everyones running. Do i need to keep tuning lower to get it to handle the music im feeding it. The other shop i went to said it sounds fine, that its just how the speaker sounds.

Edited April 4, 200817 yr by keith77

you are within FI's specs, if you know for certain that it is really 4 cubes and that it really is tuned to 32hz, then having your SSF set at 30 and your lpf set at around 80(not 150), you should be fine.

IF you are not, then one of the given specs is assumed to be off.

It could be possible if you have a very small air leak in your box that it could cause the sub to move a lot more than normal.

Opening the trunk does unload things, but I am questioning the tuning if you are having that much of an issue with that setup. How are the subs oriented??? Are they firing up into the trunk lid? If so this often loads things drastically different and can really change the tuning as well...

Keep us all posted.

Thanks,

Scott

Are you in FLA?

Let me know I'm in Ocala and can help you out!

Definitely a tuning issue, as Scott said how are things oriented in the trunk? If you've got a digital camera snap a pic and post it up.

We'll get it figured out one way or another

Thanks!

-Nick

I finally got some time to mess with the port. I tuned it down to 32hz like it was before. It sounds like the speakers are bottoming out, but I got another shop to look at them and they said it is not overexcursion, just distortion. He turned down the Xover to 80hz and he turned the gain down and it sounds a little better. The dustcaps have never got hot or smelly, the speakers just sound really distorted when i listen to them with the trunk open at 25- 30hz. When i sit inside the car it all sounds musical, 30hz is loudest (really loud) and the higher the frequency goes the weaker the bass is (60hz being not very loud). 30hz tones dont have as much excursion as the higher tones but they sound like they could be damaging the speaker. Higher tones 35-50hz sound much cleaner and have hardly any distortion. I have had audiobahn eternal 15s and Kicker L7s in a jeep cherokee and they never sounded like this, even with the back door open. Is this how they should sound. I dont want to keep playing them like this if something is wrong.

Now for the the box setup. The speakers and port are facing straight up towards the trunk lid. I know everyone says to face them back, but my last box was facing back, forward, and up and i didnt notice much of a diference. So i wanted to maximize my trunk space and have the box as big as possible. The external dimensions are H23xW24xL38 and the wood is .75" thick which makes the internal volume 10.22cuft before displacements. About .5cuft for both the speakers and .1cuft for bracing. My port is a straight slot port 4"x 22.5" with a 18" length, So that makes the port displacement 1.11cuft. The total box volume is 8.5cuft after displacements (4.25 for each speaker). The only thing that might have messed me up is carstereo.com, the calculator i used to get my tuning. Scott, Nick, or anyone who has had similar issues, if you could please look over my calculations and help me resolve this issue im having, i would greatly appreciate it.

The calculations look great. Box should be ok per the dimensions you posted. 8.5 ft^3 tuned to 32 Hz.

Little low on port area, but it should be enough that it is not acting like a leaky sealed box. . .

Do you know what frequency you are playing when they are going crazy???

How far is the trunk lid from the top of the box when it is shut? Do they bottom when the trunk is shut too?

Edited April 8, 200817 yr by BKOLFO4

The calculations look great. Box should be ok per the dimensions you posted. 8.5 ft^3 tuned to 32 Hz.

Little low on port area, but it should be enough that it is not acting like a leaky sealed box. . .

Do you know what frequency you are playing when they are going crazy???

How far is the trunk lid from the top of the box when it is shut? Do they bottom when the trunk is shut too?

The frequency where it starts sounding sloppy is around 30 hz, but When i am sitting inside with the trunk closed it sounds good. the speakers are about 5 inches from the lid. Should i try a new box with more port area?

You said above the SSF is set at 30 Hz. Are you sure it is correct? That means at 30 Hz, you should be down 3 dB already.

If I was setting it up, I would turn the SSF at the highest frequency, play 30 Hz at high volume setting, and start lowing the frequency of the SSF until just before you are over stressing the driver. Then see how it works with music. If the SSF setting is too high (music does not sound as good), you may have to tune lower or quit playing so loud with the trunk open

I know my box sounds different, and my subs act different when my rear seat is up vs. when it is folded down. . .

Brian

Edited April 9, 200817 yr by BKOLFO4

For trunk cars you will find that aiming the subs forward will sound a whole lot better than subs and port aiming up...

Aim the subs and port towards the trunk lid and you will hear a big difference in output..

Edited April 9, 200817 yr by Jybfan04

If you are playing a 30 hz tone and your box is tuned to 32 then of course it will start to bottom out, a box will not properly play a tone lower than it's tuning frequency....try a 34-35 hz tone and see if there is a problem there....if not, just don't play below 32 (which is pretty much inaudible to humans anyway)

Ive decided to build a new box. This time im going to tune at 30hz with a lot bigger port area, maybe this will fix some of the problems im running into. I think speakers facing forward sound the best also but i would lose about 2cuft of airspace to give the subs clearance. I appreciate everyones help and i will keep you posted as to how it goes.

Thanks,

Keith

Can you post up you box and port dimensions. . .

I never had problems with my BTL's going over 2" peak to peak. . .

Brian

no doubt.

i had a 15" btl off 3kw in 4.5 cubes and it took couldn't bottom out unless you went under tuning, gains set with a -6db test tone. i definitely dont see it bottoming out with a 1500w amp in 4 cubes, especially if you used a 0db test tone.

i think there is another issue, especially since you have two drivers (one with a much softer suspension, and one with a much stiffer suspension, doing the same thing)....